Miss. Code § 27-61-11
The permittee shall file a quarterly fuel use report for the preceding calendar quarter on or before the last day of the month following each calendar quarter on forms to be prescribed by the commission, or the carriers may, with the approval of the commission, furnish the required information on machine-prepared schedules. Said report shall show any information required by the commission for the administration of this chapter. Such report must be filed even though it may reflect no Mississippi miles for the quarter or accounting period. At the time of filing of each quarterly report, each permittee shall pay to the commission the full amount of the tax due on all fuel used by him in this state at the rate provided for in Section 27-61-5. The permittee in determining the fuel used by him in this state for said period may, as to each type of fuel used, determine his average number of miles of motor vehicle travel for a gallon of fuel by the use of the following formula: There shall first be determined the total miles traveled by all motor vehicles operated by permittee using a particular type of fuel; there shall then be determined the total number of gallons of such fuel consumed; the total number of gallons of such fuel consumed shall then be divided into the total number of miles traveled to determine the average number of miles of motor vehicle travel per gallon of fuel used. Proper records supporting these computations shall be maintained for a period of not less than three (3) years and shall be available to the inspection and audit of the commission. Permittee may, however, use any standards established by the commission in determining the motor vehicle travel per gallon of fuel consumed as to any particular type fuel. The permittee, in computing the amount of tax due, may take credit for all payments of the taxes levied in Sections 27-55-11 and 27-59-11, Mississippi Code of 1972, and Sections 27-55-519 and 27-55-521.
Reports and payments sent to the commission by mail must be postmarked by the due date in order to be considered timely filed, except when the due date falls on a weekend or holiday, in which case such reports and payments must be postmarked by the first working day following the due date in order to be considered timely filed.
Miss. Code § 27-61-11